Studies of patients and their families with certain genetic disorders due to chromosomal abnormalities or single gene defects. Techniques used include newly-developed chromosomal banding and differential staining, analysis of genetic markers such as enzymes or HLA within pedigrees, and dermatoglyphic analysis. Findings are correlated with phenotypic abnormalities and may be utilized for genetic counseling. Karyotypic evaluation of tissues from laboratory animals which are models of different human genetic disorders, primarily primate and murine. Relationship of cytogenetic variation to defects associated with certain diseases is stressed. Effects of gross chromosomal abnormality upon reproductive fitness and growth and development are studied.